The present invention relates to a golf club head having a structure that the strength of a shaft securing portion for securing a shaft to the body of the club head is increased and the balance of weight is improved and a manufacturing method therefor.
In recent years, the head bodies of golf club heads (hereinafter called “heads”) of golf clubs called the “woods” have widely been used, the head bodies each incorporating a hollow outer shell made of a metal material, such as titanium or stainless steel. The metal material is employed as a substitute for a general natural wood, such as a persimmon tree or a cherry tree, from viewpoints of stability of the quality and easiness of material acquisition.
Hitherto, a method of manufacturing a head of the foregoing type has been known which is arranged as shown in FIGS. 29 and 30. That is, a metal material, such as titanium, is used to mold a top member 201, a face member 203, a neck member 205 and a bottom member 211 constituted by integrating a sole portion 207 and side portion 209 with each other by forging or pressing so that a head 213 is manufactured (refer to JP-A-8-19626).
The neck member 205 has an outer shape constituted by a bevel head 215 formed into substantially a tapered curved surface having the width which is enlarged downwards and a cylindrical portion 217 formed into a pipe-like shape and integrated with the bevel head 215. As shown in FIG. 30, each periphery of the bevel head 215 and the leading end of the cylindrical portion 217 is welded to the top member 201, the bottom member 211 and the sole portion 207.
A shaft (not shown) is secured to the inside portion of a shaft securing hole 219 vertically formed in the neck member 205.
Another method of manufacturing the head (not shown) has been known with which a head body constituted by a hollow outer shell is molded by casting, and a face plate is welded to an opened face portion. A shaft securing portion is integrally molded with the heel portion of the head body. A shaft securing hole is formed in the shaft securing portion in a region from the top portion to the sole portion.
However, the cast golf club head incorporating the shaft securing portion and the head body molded integrally with each other, suffers from the following problem: the molding material is usually accumulated in between the shaft securing portion and the heel wall of the head body during the manufacturing process. Therefore, the manufactured head encounters excessive enlargement of the thickness of the portion in the vicinity of the shaft securing portion because the shaft securing portion is integrated with the heel wall. Hence it follows that the weight of the heel portion is enlarged, causing the balance of weight to deteriorate.
On the other hand, the former golf club head is manufactured by forging or press-molding, and incorporating the top member, the face member, the shaft securing pipe and the bottom member which are molded integrally with one another. The golf club head has the hollow portion formed between the heel wall of the head body and the shaft securing pipe. Therefore, the weight of the portion in the vicinity of the shaft securing portion can be reduced, causing the balance of weight to be improved. If the shaft securing pipe is welded insufficiently, there is apprehension that the welded portion is broken owing to an impact. Since a plurality of the members, such as the top member, the face member, the shaft securing pipe and the bottom member, are welded when the golf club head is manufactured, there arises a point-out problem in that greater manhours and cost are required as compared with the forged head.
A golf club head 13 has been disclosed in JP-A-10-15118. As shown in FIGS. 26 and 27, the golf club head 13 has a heel portion of a head body 1 constituted by a hollow outer shell. A shaft securing portion 5 having a shaft securing hole 3 and formed into a cylindrical shape having a bottom is, by forging, downwards molded from a top portion 9 such that a clearance is created between a heel wall 7 and the shaft securing portion 5. Moreover, a forged face member 11 is welded to an opening of the head body 1 adjacent to the face such that the forged face member 11 is disposed apart from the shaft securing portion 5.
Since the foregoing golf club head 13 has the clearance between the shaft securing portion 5 and the heel wall 7, the weight of the portion in the vicinity of the shaft securing portion 5 can be reduced.
The golf club head 13 incorporating the shaft securing portion 5 which does not reach a sole portion 15 of the head body 1, however, suffers from insufficient strength of the shaft securing portion 5. There arises another problem in that a satisfactorily large area for bonding the shaft (not shown) cannot be obtained.
In the above-mentioned structure disclosed in JP-A-10-15118, a fact is described that the lower end of the shaft securing portion 5, the heel wall 7 and the sole portion 15 may be connected to each other with connecting members (not shown). No disclosure is made about the shape and strength of the connecting member. Moreover, a satisfactory area for bonding the shaft cannot be obtained.
In JP-A-10-295857, a golf club head 29 has been disclosed which has a structure as shown in FIG. 28. That is, a cylindrical shaft securing portion 25 having a shaft securing hole 23 formed from its top portion to a sole portion 21. The cylindrical shaft securing portion 25 is integrally molded with the heel portion of a head body 17 constituted by a hollow outer shell made of a metal material, such as a titanium alloy or stainless steel. Moreover, clearance S is created between the shaft securing portion 25 and a heel wall 27 of the head body 17. However, whether or not the foregoing general structure molded by casting has not been disclosed. What is worse, a technical issue for creating the clearance S between the shaft securing portion 25 and the heel wall 27 has not been disclosed. In addition, no description has been made about the structure, operation and the effect of the structure.
The manufacturing method shown in FIGS. 29 and 30 causes a hollow portion 47 to be formed between the heel wall 220 of the head 213 and the cylindrical portion 217. Therefore, the weight of the portion in the vicinity of the shaft securing portion can be reduced, causing the balance of weight to be improved. However, there arises a pointed-out problem in that great manhours and cost are required to manufacture the golf club head because the plural elements, such as the top member 201, the face member 203, the neck member 205 and the bottom member 211, are welded to one another.
As described above, the head 213 has the structure that each of the periphery of the bevel head 215 of the neck member 205 and the leading end of the cylindrical portion 217 is welded and secured to the top member 201, the bottom member 211 and the sole portion 207. If the foregoing elements are welded insufficiently, there is apprehension that the welded portion is broken owing to an impact. There arises another problem in that use of the individual neck member 205 inhibits reliably large strength of the shaft securing portion.
On the other hand, the general head incorporates the shaft securing portion and the head body which are molded integrally by casting. Moreover, the face plate is welded to the integrated elements. In usual, the foregoing head encounters accumulation of the molding material between the shaft securing portion and the head body when the head is manufactured. Thus, the manufactured head is structured such that the shaft securing portion is integrated with the heel wall. Although the strength of the shaft securing portion can, therefore, be increased as compared with the head 213, the thickness of the portion in the vicinity of the shaft securing portion is undesirably enlarged. Thus, there arises a problem in that the weight of the heel portion is enlarged, causing the balance of weight of the head to deteriorate.
In view of the foregoing, an object of the present invention is to provide a golf club head having a structure that the strength of a shaft securing portion for securing a shaft to the body of the club head is increased and the balance of weight is improved and a manufacturing method therefor.